New stringent diesel emission regulations have had the effect of limiting the acceleration rates of turbodiesel powered vehicles. A need for supercharging of turbodiesel engines to improve their performance in the low RPM range has been recognized by most turbodiesel engine manufacturers and users. Positive displacement superchargers, such as well known Roots type and rotary type blowers driven directly by the engine via speed increasing gear trains have been utilized by major turbodiesel manufacturers. Fixed gear ratio mechanical superchargers suffer from four very undesirable features which are:
1) supercharger speed cannot practically be controlled independently of engine speed,
2) a fixed gear ratio mechanical supercharger proportions the engine intake air flow closely to the engine speed regardless of the engine load, thus the supercharger is not able to achieve the optimum air flow to fuel ratio at all engine loads,
3) a mechanical clutch is required to disconnect the blower from the engine when not needed which result in an abrupt change in boost, and
4) the positive displacement blower blocks the air flow through it when disconnected from the engine.
The applicant has been issued U.S. Pat. No. 5,421,310 for a hydraulic supercharging system utilizing a miniature, very high speed hydraulic turbine driving a compact centrifugal compressor to supercharge a turbocharged engine. The advantage of this system is its ability to modulate the supercharger speed independently of the engine speed and thus achieve the optimum boost and air/fuel ratio at most engine loads and speeds. It utilizes a "stand alone" relatively simple hydraulic system incorporating the bearings lubrication and seals functions. This hydraulic supercharging system does, however, require a separate fluid system which may be undesirable is some applications.
What is needed is a system which provide some of the advantages of the hydraulic system without need of a separate fluid system.